Traditional cold packs used to transfer heat from mammalian skin utilize either a chemical reaction or a refrigerator/freezer to chill a substance, which is usually water or gel. These packs are difficult to use because, for example, a refrigerator is not portable. Therefore, if a user wants a cold pack, he or she must travel to the refrigerator to extract the pack. Furthermore, the user has no control over the temperature of the cold pack other than by controlling the temperature of the refrigerator, which may not be convenient.
Traditional hot packs are problematic in that they typically require an electrical connection, as may be the case with a heating pad, and offer poor temperature regulation.